Title

Author

Date of Graduation

Document Type

Thesis

Degree Name

Bachelor of Science

Degree Level

Undergraduate

Department

Health, Human Performance and Recreation

Advisor

Ganio, Matthew S

Reader

Kavouras, Stavros A

Second Reader

Fort, Inza L

Abstract

"Purpose: Previous research shows dehydration decreases sweating and skin blood flow during heat stress but it is unknown whether these decrements are from pre-synaptic (i.e. central nervous system) or post-synaptic (i.e. sweat gland/blood vessel) alterations. The purpose of this study was to determine whether dehydration affects post-synaptic sweating and skin blood flow responses. We hypothesized that dehydration will negatively affect post-synaptic sweating and both endothelium-dependent and independent vasodilation. Methods: 12 males (age= 25 ± 3 y, height = 178.4 ± 5.1 cm, body mass = 75.9 ± 10.9 kg) participated. 24 h before each trial, subjects were passively heated for ~2 h. In the euhydrated trial, subjects were given water to maintain euhydration and were encouraged to maintain hydration for the remainder of the day. In the dehydrated trial, subjects were not given any fluids during passive heating and were fluid restricted for the remainder of the day, which lead to a 2.2 ± 0.7 % body mass loss. Hydration status was confirmed by urine specific gravity (USG) and urine osmolality (UOSM) at the time of testing; dehydrated individuals had a USG >1.020 and a UOSM >700 mOsm/kg (mmol/kg). Seven incremental doses of sodium nitroprusside (SNP; induces endothelium-independent vasodilation; 5x10-8 to 5x10-2 M at 10-fold increments) and methylcholine (MCh; induces local sweating and endothelium-dependent vasodilation; 1x10-7 to 1x10-1 M at 10-fold increments) were administered via two subcutaneous fibers in the forearm (i.e. microdialysis). Local sweat rate (LSR) via ventilated capsule and cutaneous vascular conduction (CVC) via Laser Doppler were recorded over the site of drug administration at the last minute of each dose. At the end of the 7th dose, maximal vasodilation was elicited by delivering a maximal dose of SNP for 10 minutes followed by local heating of the skin (~44°C) for 30 min; all CVC data are expressed as %max CVC. A 2 (hydration) x 8 (dose) repeated measures ANOVA was used to evaluate the effect of dehydration on sweating and CVC responses. Paired t-tests were used to compare hydration biomarkers between trials. An alpha of 0.05). Discussion: The hypothesis that dehydration negatively affects post-synaptic sweating and both endothelium-dependent and -independent vasodilation was not supported. Dehydration did not affect post-synaptic LSR and endothelium-independent or -dependent CVC. These findings suggest dehydration decreases sweating and cutaneous vasodilation via central mechanisms. "